Bark beetles such as the Mountain Pine Beetle—Dendroctonus ponderosae Hopkins, Western Pine Beetle—Dendroctonus brevicomis LeConte, Spruce Beetle—Dendroctonus engelmanni Hopkins, Douglas-fir Beetle—Dendroctonus pseudotsugae Hopkins and the Southern Pine Beetle—Dendroctonus frontalis Zimmermann, under ideal conditions, can devastate vast areas of forests.
After boring into the target trees, mated adults dig galleries or channels under the bark where eggs are deposited. These eggs hatch into larvae which then feed on the cambium layer beneath the bark, creating channels which cut off the supply of water and nutrients, thereby killing the tree. The larvae then pupate beneath the bark and finally adults emerge from the pupa chamber by boring out through the bark. The disruption of the cambium layer causes the tree to die much as it would if this area was ‘ringed’ or cut through with an axe or saw.
The beetles carry one or more types fungi on their bodies and, when this fungus germinates within the tree, it spreads and limits the natural uptake of nutrients while turning the wood blue in colour. The damage done by the insects along with the blue stain has the effect of drastically lowering the value of lumber harvested under these conditions. Destruction of conifers, for example, pine, spruce and Douglas fir, by boring bark beetles not only costs the forestry industry, the dead trees also pose a significant fire hazard. Added to the above mentioned costs, additional expenses are involved with replanting damaged areas.
Because the beetles spend the majority of their life cycle protected under the bark of the infested tree, conventional chemical pesticides, applied by traditional methods are of little use.
U.S. Pat. No. 5,281,418 teaches methods and compositions for combating mountain pine beetle (Dendroctonus ponderosae) comprising deploying verbenone (4,6,6-trimethylbicyclo[3.1.1]hept-3-en-2-one) from controlled-release devices on or near pine trees. It is of note that it is stated that this compound deters beetle attack on trees but does not disrupt the life cycle of the beetle.
U.S. Pat. No. 4,994,268 teaches the use of pheromones as bait to lure beetles away from specific areas or to keep beetle infestations localized.
U.S. Pat. Nos. 6,051,612 and 6,217,891 teach a method of repelling beetles comprising applying mixtures of bark volatiles from non-infected trees to pine trees in an effort to confuse the beetles and prevent infestation.
Another method of control consists of spraying individual trees with deterrents or insecticides, an expensive and risky solution due to environmental concerns over toxic chemicals. Furthermore, in order to be effective, the insecticide must be able to penetrate the bark of the tree, as discussed above.
Yet another method of control consists of applying monosodium methane arsenate to a continuous shallow cut around the base of a tree. Normal translocation of the compound kills the beetle and its larvae, but the axe cut also kills the tree.
Other methods known in the art for stopping the spread of beetle infestations include sanitation harvesting, wherein infested trees are harvested; fall and burn, wherein infested trees are burned to prevent spreading; and injecting infested trees with pesticide, which is laborious and time-consuming.
As can be seen, the prior art teaches mainly methods of attempting to prevent or contain infestation, not destroying the beetles themselves. As discussed above, other methods require that insecticide be injected into the bark or sections of the bark be removed for application of insecticide, which is time-consuming and potentially damaging to the tree. Thus, the above methods are expensive, labour intensive, and for the most part ineffective. Clearly, an composition for treating and/or preventing boring bark beetle infestations which can be easily and economically applied directly to the barks of trees is needed.